Computer programs may be arranged to run or take some particular action when certain conditions are met. For example, a computer system may be configured to run a backup program and/or system maintenance program every weeknight starting at nine o'clock. A payroll application may be run twice a month, and a check-printing program may run when the payroll program completes. A batch system may be employed to launch such jobs when events indicate that conditions for executing each of those jobs are met.
One event system allows subscribers to register with a centralized event service for notification of specified events. As each event is received at the event service, the event service matches the event with one or more subscribers registered for that event, and fires the event to the appropriate subscriber or subscribers.
However, while such an event system is acceptable in some environments, it cannot meet the demands of a large-scale enterprise computing environment, wherein events need to be handled on the order of one-hundred events per second. At present, existing event handling systems are unable to satisfy the amount of event handling needed in a large-scale enterprise computing environment.
Security is another issue of concern to large-scale enterprise computing. For example, with existing systems, it is possible for a malicious user to tap into an event, whereby the event could be used to trigger an undesirable action, such as erasing needed data. Similarly, if an event's information is modified, whether intentionally or inadvertently, the event is likely to cause unpredictable behavior that may be damaging. Another related issue is access-control as to which job (or who) may trigger a particular job, and which jobs may consume a particular event. For instance, the ability to start a job that pays bonuses needs to be secure. Similarly, the fact that a sensitive job has completed, along with its status, should be guarded.
Reliability is also a key requirement that cannot be met by existing event services. For example, payroll needs to be run as scheduled, as the adverse consequences of failing to do so on time can be readily appreciated. However, if the event that triggers the running of the payroll application does not arrive, the payroll application will not be run, at least not without manual intervention following recognition that the program is not executing when it should be. Similarly, payroll should not be run more than once per pay period, e.g., two events that trigger the payroll application should not be received in the pay period. However, existing event services do not guarantee that events will be delivered, and delivered exactly once, i.e., there is a possibility that events may be duplicated or dropped.
In short, existing event services are unable to meet the scalability, security and/or reliability requirements needed by large-scale enterprise computing environments. As a result, batch systems and the like that operate based on conditions being met are run on a per-server basis, not across a network. At the same time, smaller scale computer networks also would benefit from increased reliability, security and scalability that have been heretofore unavailable in event handling systems.